In recent years, active researches have been conducted on variable resistance elements that store information using a storage function of a variable resistance layer.
The variable resistance layer used for the variable resistance element is a thin film including a material mainly made up of a metal oxide. A resistance value of the variable resistance layer changes in response to an application of a voltage pulse to the variable resistance layer, and a resultant resistance value is held in a nonvolatile manner. When a high resistance state and a low resistance state of the variable resistance layer correspond to binary data “1” and “0”, respectively, the binary data can be stored in the variable resistance element.
The magnitude of a voltage applied to the variable resistance element for causing a resistance change or the magnitude of a current flowing according to the applied voltage are only necessary to be a degree sufficient to cause a physical state of the variable resistance layer to change and not to damage the variable resistance layer, and a voltage pulse of such a magnitude may be applied more than once.
A memory cell array of a so-called cross point type can be configured by providing a memory cell including the variable resistance element in corresponding one of three-dimensional cross points of a plurality of word lines and a plurality of bit lines.
It is known that, with the cross point memory cell array, when data is written into a selected memory cell (selected cell) or data is read from a variable resistance element, a disorder which is called a write-disturb or a read-disturb may occur, by which data of a memory cell that is not selected (non-selected cell) is caused to change due to an influence from a leak current flowing through the non-selected cell.
In view of the above, nonvolatile storage devices using a cross point memory cell array are generally configured such that the write-disturb and the read-disturb can be prevented.
A non-volatile store device including a memory cell array in which memory cells including a serial circuit of a variable resistance element and a diode (a current steering element) are arranged in a matrix has been proposed as an example of a nonvolatile storage device which is capable of suppressing the occurrence of the read-disturb using a cross point memory cell array (see PTL 1, for example).
The non-volatile storage device disclosed by PTL 1 includes a memory cell array which uses, as a memory cell, a non-volatile storage element including a variable resistance element and a diode connected to each other in series, and each of the ends of the memory cell is connected to a corresponding one of a word line and a bit line.
Data is read from a selected cell via the word line and the bit line to which the selected cell is connected, by applying a predetermined reading voltage (a voltage equal to or greater than an on-voltage of the diode) to the selected cell.
A voltage intermediate between a voltage applied to the word line to which the selected cell is connected and a voltage applied to the bit line is applied to a word line and a bit line which are not connected to the selected cell. More specifically, approximately half a reading voltage is applied to a non-selected cell (a half selected cell) connected to the word line or the bit line to which the selected cell is also connected.
Thus, when the reading voltage is set at a value smaller than twice the on-voltage of the diode, a voltage applied to the half selected cell is smaller than the on-voltage of the diode, and thus a leak current from the half selected cell is suppressed to a minute level due to a nonlinear voltage current characteristic of the diode. This prevents the read-disturb.